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Author Topic: RXD pin of FT232R and FT232H is HIGH when not connected  (Read 18093 times)

brumbarchris

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RXD pin of FT232R and FT232H is HIGH when not connected
« on: March 20, 2024, 05:01:36 pm »

Hello,
I have two FTDI cables based on the FT232H (a C232HMDDHSL-0 and a C232HD-DDHSP-0) and one based on the FT232R (TTL-232R-3V3).

In active mode (device enumerated after EEPROM read) the RXD pin is HIGH on these devices (some 2.5V on the FT232H based cables and 3.3V on the FT232R based cable). Now, in this mode, this pin operates as an input. In order to be high, it must have a pull-up. Is there any information available with regards to this pull-up (its value)?

The datasheet of the FT232R might infer the presence of a 200k pull-up on this pin, with this statement which is present after Table 5.10:
Quote
** Only input pins have an internal 200KΩ pull-up resistor to VCCIO

But there is nothing on this in the FT232H datasheet (although it talks about pull-ups on various other pins, the RXD pin is not mentioned).

I am familiar also with AN_184 FTDI Device Input Output Pin States, but that didn't help either, it just indicates that in in active mode the RXD pin is configured as "Function".

Regards,
Cristian
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FTDI Community

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Re: RXD pin of FT232R and FT232H is HIGH when not connected
« Reply #1 on: March 21, 2024, 10:48:38 am »

Hello,

Yes, there are internal pullups on the RXD lines of FT232R and FT232H.

the typical value is 75 KΩ. You can find more information in 5.3 of the FT232H datasheet.

Best Regards
FTDI Community
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brumbarchris

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Re: RXD pin of FT232R and FT232H is HIGH when not connected
« Reply #2 on: March 21, 2024, 12:21:42 pm »

Thank you.

Cristian
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